Gastrulation, Neurulation (wk 3) Flashcards
Gastrulation is the beginnings of
Morphogenesis
What occurs during gastrulation?
Changes to the bilaminar disc
- appearance of the primitive streak
- development of the notochord and prechoridal plate
- differentiation into 3 germ layers
- trilaminar embryonic disc
Once the trilaminar disc is formed, what is the embryo referred to as
A gastrula
Week 3 development
Germ Layers (3):
Ectoderm
Mesoderm
Endoderm
Ectoderm
Surface ectoderm-epidermis
Neuroectoderm - CNS, PNS, retina
Mesoderm
Skeletal and smooth muscle, CT., most of cardio system, blood cells, bone marrow, reproductive and excretory organs
3 parts of the mesoderm
Paraxial = somites Intermediate = genitourinary systems Lateral = body walls
Endoderm
Epithelium of respiratory and GI systems, including glands
Primitive streak is what
A thickened linear band of epiblast
The primitive streak begins where
Caudally in the median plane of the embryonic disc
The primitive streak is formed by what
A migration of epiblast cells to the median plane of the embryonic disc
What happens when the primitive streak elongates
The cranial end enlarges to form the primitive node and the primitive groove
The primitive groove ends in a small depression which is called the
Primitive pit
Epiblast cells migrate through the primitive groove to become the
Endoderm and mesoderm
All of the primitive stuff together forms the embryo’s
Craniocaudal axis
Cells from the deep surface of the primitive streak forms the embryonic connective tissue known as
Mesenchyme
Mesenchyme forms many types of cells:
Fibroblasts
Chondroblasts
Osteoblasts
The primitive streak decreases in size and becomes an insignficant structure where
In the sacrococcygeal region of the embro (wk 4)
The prechordial plate forms when
What is it?
What is it the site of?
Day 14
Endodermal cells in a localized area that form a thickened circular area
This is the site of the mouth
Notochordal process forms when
Day 16-17
Mesenchymal cells form a cord called the notochordal process
As the notochordal process grows cranially it develops a lumen called
The notochordal canal
The notochordal process continues to grow until
It reaches the prechordal plate
What does the notochord provide
Defines the axis of the embryo
Gives it rigidity
Serves as the basis for development of the axial skeleton
The future site of the vertebral bodies form around what
The notochord
The notochord deteriorates as the vertebral bodies form
Remains as the nucleus pulposus
What induces neural plate formation
The notochord
How does the mesoderm and endoderm form?
Epiblast cells pass through the primitive streak
Triggered by embryonic growth factors
3 types of mesoderm:
Paraxial =somites
Intermediate = genitourinary systems
Lateral = body walls
Oropharyngeal membrane is formed how?
What does it prevent?
Future site of?
Formed from the prechordal plate
The endoderm and ectoderm fuse
Prevents the notochordal process from continuing cranially
Future site of the mouth
The cloacal membrane forms where and is the future site of what?
Forms caudally to the primitive streak
Site of future anus
Cardiogenic area is what?
Premordium of the heart
Allantosis appears when?
Shape?
Involved with?
Forms what?
Appears approx day 16
Sausage shaped - extends from caudal wall of umbilical vesicle to the connecting stalk
Involved with early blood formation
Forms the early urinary bladder
The vessels become unbilical arteries and veins
The neural plate forms from the thickening of what?
Forms the?
The notochord growth induces the embryonic ectoderm thickens forming the neural plate
Forms the CNS - neuroectoderm
Neural grove forms when, how, and what?
Day 18
Neural plate opens in center
Neural folds form on each side of grove
Beginning of the brain!
Neural tube begins forming when?
End of week 3
Neural folds come together and fuse
Folic acid plays a part in this
Neural crest cells fuse to form what
The neural crest between the neural tube and ectoderm
Somites begin forming when?
How?
Forms what?
Begin forming end of week 3
The paraxial mesoderm begins dividing into paired cube shaped bodies called somites - around the neural tube
Starts in the occipital region
Forms most of the axial skeleton - associated with musculature and dermis
Each somite is innervated by what?
1 individual spinal nerve
Somites differentiate into 2 regions:
Sclerotome - ventraomedial part, form axial skeleton
Dermomyotome - dorsolateral part w/ 2 regions
Myotomes and dermatomes of the same somite are innervated by what
The same spinal nerve
Myotomes differentiate into two regions:
Epaxial - muscle innervated by dorsal primary rami, deep muscles of the back
Hypaxial - muscle innervated by ventral primary rami, all other muscles
Each individual spinal nerve separates into what
Dorsal and ventral primary rami just outside of the IFV
Lateral mesoderm forms the
Body walls
Lateral mesoderm differentiation causes the development of the
Intraembryonic coelom
- small coelomic spaces in lateral mesoderm and cardiogenic mesoderm forming a single horseshoe shaped cavity
Development of the intraembryonic coelom divides the lateral mesoderm into 2 layers called:
Somatopleure - the somatic or parietal
Splancnopleure - splanchnic or visceral
When does the circulatory system begin?
Beginning of wk3
When does uteroplacental circulation begin
Wk 5
Angiogenesis begins where?
When?
Begins in the extraembryonic mesoderm of the umbilical vesicle, chorion, connecting stalk
Wk3
Mesnechymal cells differentiate into
Angioblasts
Angioblasts form clusters known as
Blood islands
Angioblasts flatten to form what
Primitive endothelial cells
The mesenchymal cells that surround the primordial endothelial blood vessels differentiate into what
The muscular and connective tissue elements of the vessels
Vasculogenesis is the formation of
New vascular channels by assembly of individual cell precursors (angioblasts)
Primordial blood cells develop from hematopoietic progenitor that form from specialized endothelial cells of vessels called
Hemangioblasts - located on the umbilical vesicle and allantois
What is hematogenesis
When does it begin
Where does it begin
Blood formation
Week 5
Beginning in liver, then in spleen, bone marrow, lymph nodes
Mesenchymal tissue in cardiogenic area forms what
Heart and great vessels
Primitive heart tube contains what and forms what
Contains endothelium-lined channels = endocardial tubes
Fuse to form a primordial heart tube
How does the primordial cardiovascular system form?
The tubular heart joins with blood vessels in the embryo, connecting stalk, chorion, and umbilical vesicle
What is the first organ system functioning?
At end of week 3 the blood is circulating and heart is beating
Trancus arterious
Premordium of the aorta and pulmonary trunk
Bulbus cordis
Forms the primitive ventricle and part of the aorta
Sinus venosus
Premordium of the SCV IVC some coronary veins and atria
Development of chorionic villi
Early wk 3
Mesenchyme grows into the primary villi
Forms a core of loose connective tissue
This is secondary villi
When do primary chorionic villi appear?
At end of second week
Cytrotrophoblastic cells produce cellular extensions that grow into the overlying syncytiotrophoblast forming it
What happens to mesenchymal cells in the secondary villi?
They differentiate into both capillaries and blood vessels
When capillaries become visible the villi are called
Tertiary chorionic villi
The capillaries fuse to form
Arteriocappillary networks
The capillary network is connected to the embryonic heart by vessels that differentiate from what
The mesenchymne of the chorion and connecting stalk
Lacunae does what
The maternal blood flows into it
Oxygen and nutrients are passed to the embryo tissues over the surface of synchytiotrophoblast
Oxygenated blood passes into the lacunae from what
The spiral endometrial arteries in the endometrium
Deoxygenated blood is removed from the lacunae through what
Endometrial veins
When is fetal blood flow established
End of 3rd week
Heartbeat is present at day what
21-22
When can the heartbeat be detected
During 4th week
Cytotrophoblastic shell is formed by what?
Cytotrophoblastic cells of the chorionic villi
Main stem chorionic villi
Attach the villi to the endometrium
Branch chorionic villi grow from
The sides of the main stem chorionic villi
Most of the exchange of material between blood of the mother and the embryo takes place through
the walls of the branch chorionic villi
2 regions of the dorsolateral part, aka the dermomyotome
Myotome - myoblast - form muscle
Dermatome - fibroblast - form dermis
